The invention relates to a method for temperature compensation in measuring systems which can also be part of an item of equipment, that are dependent on the operating temperature, and whose temperature dependency is caused by one or several temperature-sensitive components with a temperature coefficient, and that can be operated electronically or are linked thermally with a neighboring electronically driven component which is already required for the measuring system.
Numerous measuring systems such as, for example, an extinction sensor in washing machines, a light barrier in cash dispensers or pressure sensors in motor vehicles, contain temperature-sensitive components which behave differently at different temperatures. Especially in mass goods such as household appliances or motor vehicles, simple temperature-dependent components are used which display a high temperature sensitivity. For these applications, simple calibration or compensation methods are necessary that can best be performed at low cost in the microprocessor control that is provided in the item of equipment itself. In known systems, either the individual parts or the complete system are measured in terms of temperature sensitivity with respect to the measured quantity for the purpose of temperature compensation and stored in a variety of forms (table value, selection, EEPROM, etc.). When applied at a later time in the equipment, the derived values can be used in calculations if the ambient temperature is measured at the same time. As a rule, a typical or even a specific value is stored here for the temperature-sensitive components and this is taken for later calculations. The method for measuring the specific temperature sensitivity consists of measuring the temperature coefficients of each temperature-sensitive component before the equipment or measuring device is put into operation. In this method, the components are heated by a separate heating system and the results obtained at the different temperatures are stored as temperature coefficient, as characteristic curve, or as a pair of values.
However, in the subsequent calculations for temperature compensation it has been found to be very cost favorable if the typical temperature sensitivity as specified by the manufacturers of such temperature-sensitive components is used.
Another method for temperature compensation consists of heating the temperature-sensitive components, the measuring device or even the entire equipment up to a fixed operating temperature that is always higher than the ambient temperature which might prevail. This heating up process to the firmly defined operating temperature is performed by the heating device. This heating device is provided solely for the purpose of heating and has no further function for the subsequent measurements or for the equipment as is the case, for example, in heated quartz oscillators.
A disadvantage with this method, however, is that when measuring the temperature sensitivity in each individual measuring system the production times for the measuring system lengthen enormously when external heating is applied on account of the large thermal time constants. All methods described here are either very expensive, very inaccurate or very elaborate and the long-term behavior of the temperature-sensitive components is not allowed for. Here too, external components are required that must also be placed in the equipment simply because of their heating capability.